A conventional technology discloses a method for reducing a tilt of the reading/writing surface of a disc relative to the optical axis of a beam. In the method, information concerning the tilt of the reading/writing surface of the disc opposite to an objective lens is detected, and based on the information, the objective lens is tilted.
Patent Document 1 discloses a tilt control method. According to the method, when making various types of adjustments, such as an adjustment of a laser power with respect to the disc mounted in a disc drive, a laser beam is emitted by shifting an objective lens by a predetermined amount with the optical head at a position to be adjusted and at a disc rotation speed to be adjusted, and the relationship between a shift amount of the objective lens and an offset of a push-pull tracking error signal is learned, so that the learned relationship is maintained during reading/writing.
[Patent Document 1] JP Patent Publication (Kokai) No. 2003-217153 A